Process for pickling metals



' removes oxides, such as rust and the like, and

flit

Patented Oct. 17, 1939 PROCESS FOR PICKLING METALS Robert 1. Brandt, New York, N. Y., assignor to Colgate-Palmolive-Peet Company, Jersey City, N. J., a corporation of Delaware No Drawing. Application January 20, 1938, Serial No. 186,605

10 Claims.

The present invention relates to solutions for and processes of pickling metallic surfaces such as iron, steel, nickel, copper, bronze, yarious a1; lgys, and the like, for removing rust, mill scale, handling marks, and oxides of various natures therefrom, and more particularly to the addition of certain derivatives of petroleum to such solutions for the purpose of improving the same.

In the prior art, it has been customary to use mineral acids, such as s lphuri mgng, and phosphoric acids or the lik pickling baths, yet it has been recognized for years that these ordinary pickling methods are highly wasteful and have in many instances produced extremely detrimental eifects, such as pin holes and roughened surfaces in the metal. This has been due in the main to the relatively rapid attack of the acid upon the metal and the resulting non-uniform treatment. Thus, the acids not only react with the oxide layer to be removed, but also with the metal itself, with the result that a pitting of the metal surface occurs, especially where scaling has exposed bare patches of metal. Moreover, it has been observed that acids such as the above cause an undesirable brittleness in the metal as a result of the formation of pockets of hydrogen gas between the layers of the scale and the surfaces of the metal.

An important object of the present invention is the provision of a pickling bath which adequately other undesirable formations, and at the same time wastes less of the metal in the pickling solution without shortening the time customarily required by the usual mineral acid baths for the same class of work. A further object of the invention is to provide a pickling bath which has a uniform action on the metal, less metal being actually dissolved, and produces a smoother finished surface, i. e. which has the effect of producing a surface on the metal that is substantially devoid of irregularities or pitted areas, such as are usually obtained when cleaning metals in ordinary mineral acid pickling baths under similar conditions. A further object of the invention is to substantially inhibit all corrosion of the metal resulting from the action of the pickling bath, either while the metal is in the bath or after removal therefrom, and a still further object is to avoid the formation of hydrogen pockets, thereby preventing the pickled metal from becoming brittle.

The present invention resides broadly in using as metal pickling baths relatively dilute aqgg u s, in

organic pickling acids, such as oxalic, tartaric, and citric acids, and small quantities of certain substances which have been found capable of effectively reducing or even totally preventing the attack of the metals by the acids, although not hindering in any way the removal of the oxides or other similar materials from the surfaces thereof. These substances, constituting inhibitors, may be prepared in numerous ways, some of which will be hereinafter described. For a more complete disclosure of their nature and preparation, however, reference is made to my copending applications, S. N. 117,096 and S. N. 138,463, now issued as Patents Nos. 2,149,661 and 2,149,662, as it is considered sufficient for the purposes of this invention to outline the more important details of their manufacture only.

According to the methods for the most part described in Patent No. 2,149,661, the mineral oil to be treated, preferably a lower viscosity raw distillate of a naphth ene base crude, such as a Texas Gulf Coast Crude, is first extracted with liquid sulphur dioxide, liquid sulphur dioxide plus benzol, or other preferential solvent, such as furfural, phenol, nitrobenzene, or the like. The extracted material is then dissolved in liquid sulphur dioxide, or, when the extracted material is already in sulphur dioxide solution as a result of the sulphur dioxide solvent extraction process, the next step may consist in diluting the solution with as much liquid sulphur dioxide as may be necessary to prepare for the subsequent steps in the process, usually with from one to two times the volume of extracted material, it being understood that the presence of sulphur dioxide as a diluent permits rapidity of contact and lower operating temperatures and also exerts a catalytic effect on the reaction. The resulting solution is then cooled, say to 15 C., and mixed with a sulphonating agent, such as fuming sulphuric acid, sulphur trioxide, chlorsulplicfiicacidprthe like'jpreferably in solution in liquid sulphur dioxide, while vigorously agitating and keeping the temperature quite low, preferably below 5 C. Upon completion of the mixing and after the evolution of heat has substantially ceased, the reacting mixture is usually raised to a temperature somewhat higher than that at which the original mixing took place, for example +5 0., and the agitation continued for a sufficient length of time to complete the reaction. The original mixing is ordinarily accomplished in a few minutes, after which the agitation may be continued for a period varying from a few minutes to an hour and a half, and sometimes as high as three hours. When the treatment with the sulphonating agent has been com- .c -L -v;

pleted, the sulphur dioxide is removed by evaporation, preferably at or below the treating temperature, and the remaining material is diluted with cold water, generally with twice its volume, while preferably keeping the temperature below about 20 C. The resulting product is then preferably washed with a low boiling hydrocarbon solvent, such as Pennsylvania grade saturated gasoline, which is not only easily removable but is capable of readily dissolving any impurities or products of undesirable side reactions, subh as resins, polymerized hydrocarbons, coloring matter, oil oluge sulphonic acids, thio compounds and the like. The; methds described in Patent No. 2,149,662 are similar in many respects to the procedure outlined above but include certain additional steps whichmaybe carried out either before or after the extraction, although it is prefered to carry them out after the extraction. For example, the boiling range of the portion of the oils to be sulphonated may be further narrowed by additional fractionation of the oil after extraction or by additional or more specific fractionation prior to extraction and discarding the fractions from at least one end of the boiling range. Also the oil to be used for sulphonation may be treated, at any time prior to the sulphonation, with caustic soda to remove certain undesirable acidic substituents, with sulphuric acid to remove asphalt-like and highly reactive bodies and water, and with contact clay to assist in sludge removal. It is also proposed varying the extraction step itself somewhat, as by keeping the temperature relatively low during that phase of the process, i. e., between about 15 C. and +15 C.

As an example of one of the methods described in Patent No. 2,149,662, a distillate from Texas Gulf Coast crude boiling between 130 C. and 350 C. at 5 mm. pressure and having a Saybolt viscosity of seconds at F., may be countercurrently extracted with approximately an equal volume of liquid sulphur dioxide by the usual Edeleanu process, the sulphur dioxide separated from the extract and the extract then fractionally distilled, in vacuum, in the presence of about 0.1% of its weight of caustic soda. The fraction boiling between 220 and 240 C. at 5 mm. pressure may be treated with about 1% of its weight of 92% sulphuric acid by mixing it therewith for about forty-five minutes. Most of the sludge will settle out at once, but the remainder, which is known as pepper sludge has a tendency to remain in suspension and it will usually be found desirable to remove this sludge by treating the material containing the same with an amount of contact clay in the neighborhood of 0.2% by weight of the material being treated, and then heating the mixture to to C. while out of contact with air. Upon filtering, the oil will be found bright and clear.

The desired fractions of the extract having been obtained, they may individually or collectively be sulphonated by dissolving them in approximately from one to two times their volume of liquid sulphur dioxide, cooling to around -15 C. and adding, over a period of about 15 minutes, an amount of 20% oleum about equal in weight to that of the material to be sulphonated, the oleum being preferably first dissolved in liquid sulphur dioxide. Vigorous agitation is practically a necessity during this operation and the use of a jacketed autoclave, provided with a stirring device, thermometer and pressure gauge has been found desirable. Considerable heat is evolved during and immediately after the addition of the acid, but temperature control can be maintained by circulating a cooling fluid through the jacket. The temperature should preferably not be permitted to rise above about 5 C. After the acid addition, the temperature should be allowed to rise to +5 C., and maintained at that point for about one and a half hours to three hours, depending on the type of oil, the agitation being continued. At the end of this period the sulphur dioxide may be separated as a vapor, by releasing the pressure at a temperature below +5 C.

To finish the preparation, the substantially sulphur dioxide free material may be mixed with twice its volume of ice-water, keeping the temperature below +20 C. There is a considerable amount of heat evolved at this step on account of the heat of dilution of the acids. After dilution, the aqueous solution or dispersion should be immediately batch-washed several times with 20% of its volume of gasoline, all of which is volatile below 250 F.

Although it has been found preferable to employ the above described substances in the form of acids, considerable inhibiting eflect may also be obtained by adding the salts of the acids to the pickling baths, particularly the salts obtained by neutralizing the various sulphonic acids with basic compounds such as caustic soda, soda ash, ammonia, triethanolamine, lime, and the like. The marked inhibiting effect obtained by utilizing either the sulphonic acids or their salts may be readily seen upon referring to the results of certain tests which will be hereinafter described.

According to one test, pieces of polished boiler plate were subjected to the action of acid mixtures containing varying quantities of sulphuric acid and one or a mixture of the sulphonic acids prepared as described above. In all cases, the pieces of metal were treated with acid mixtures having a total acid concentration of 5%, the treatment being carried out for ten minutes at 180 F. The percent loss of metal resulting from the sulphuric acid in the presence of varying amounts of sulphonic acid was as follows:

Percent Percent Percent Total acid concentration (in per- H1804 sulphonic loss of oentage) in total acid in metal acid total acid 100 Zero 0. 40 95 5 0.03 85 15 0.025 75 25 0. 025 50 50 07 02 15 85 0.01

According to another test, a 25% solution of sulphuric acid was used. in each case, and to these solutions were added varying quantities of the sodium salt of the sulphonic acid, containing approximately 50% active ingredient, the treatment being carried out at 82 F. for a period of two hours. The percent loss of metal resulting from the sulphuric acid in the presence of varying amounts of sulphonate was as follows:

In the above tests the metal samples pickled without the addition of sulphonic acid or sulphonate were dull gray in color and very much corroded. The samples treated with sulphonic acid or sulphonate, however, were bright and shiny and thoroughly pickled, all oxides, rust, and the like being removed, and showed far less loss in weight. Moreover, it has been found, in general, that as a result of the uniform treatment the finished surfaces of metals pickled as described herein do not become pitted or otherwise roughened, and are smooth in contrast to the surfaces obtained with ordinary mineral acid baths under the same or similar conditions. The development of the so-called pickling fumes, which are so dangerous in view of their poisonous nature and inflammability and otherwise undesirable in view of their deterioration effect, is also substantially avoided.

In addition to being excellent inhibitors for use in mineral acid pickling baths, it has been found that the sulphonic acid compounds and derivatives described herein and in my patents noted above possess considerable value as pickling agents, per se, and that admirable results may be obtained by using various amounts of these substances in the form of acids, while entirely omitting mineral acids, or the like. Such baths, however, are not as efficient as the baths constituting the primary subject of the present invention, i. e., those utilizing the sulphonic acid compounds as inhibitors.

In this specification the term sulphonation has been used in a broad sense to mean the reaction of sulphuric acid upon the oil products and not merely the formation of one class of chemical compounds. Furthermore, the details of the sulphonation process, such as the quantities of the reagents, their concentrations and the time period and temperatures for the reaction are but examples of satisfactory constants for a particular type of oil. As the type of oil is varied, as it may be within the scope of this invention, these various factors will necessarily vary, but the application of the general principles set forth herein, and the varying of these factors in accordance with the needs of the particular situation are within the concepts of this invention. Also, it is to be understood, that although my previously mentioned patents refer primarily to batch methods of preparing the sulphonates, the operations described therein may be readily carried out in a continuous manner, which will be apparent upon examining the flow sheets contained 0 in Patent No. 2,149,662.

It is also to be understood that the usefulness of this invention as applied to pickling metals is not predicated upon the quantities, temperatures, and other operative conditions employed in carrying out the above tests, as it will be apparent to those skilled in the art that the relative effectiveness of the various pickling baths necessarily depends to some extent upon the type and surface condition of the metal being pickled as well as upon the concentration and temperature of the pickling bath, and that the various operative conditions may be advantageously changed to suit the needs. Thus, it is within the scope of this invention to employ varying amounts of either the mineral acid pickling agent or the sulphonic acid or salt constituting the inhibitor, as well as to change the temperature of the pickling bath and the duration of treatment, such variations being readily accomplished with continued good results.

I claim:

1. A process of pickling ferrous metals which comprises treating said metals with a solution of an organic acid suitable for pickling to which has been added a small proportion of the reaction product of a material obtained from a mineral oil by solvent extraction and a sulphonating agent, which product was made in solution in liquid sulphur dioxide.

2. A process for pickling ferrous metal surfaces which comprises treating the surfaces with an aqueous solution of an acid consisting of the reaction product of a material obtained from a mineral oil by solvent extraction and a sulphonating agent, which product was made in solution in liquid sulphur dioxide.

3. A pickling bath for metals which are easily oxidizable or corrodible comprising an aqueous solution of an organic acid suitable for pickling to which has been added a small proportion of the reaction product of a material obtained from a mineral oil by solvent extraction and a sulphonating agent, the reaction having taken place in solution in liquid sulphur dioxide.

4. A pickling bath for surfaces of ferrous metals consisting essentially of a water solution of the reaction product of a material obtained from a mineral oil by solvent extraction and a sulphonating agent, the reaction having taken place in the presence of liquid sulphur dioxide.

5. A process for pickling ferrous metals which comprises subjecting said metals to the action of an acid pickling bath containing a small proportion of a product made by extracting petroleum products with liquid sulphur dioxide and thereafter treating the extracted material with a sulphonating agent while dissolved in a substantial proportion of liquid sulphur dioxide.

6. A pickling bath for ferrous metals which comprises an aqueous solution of an acid suitable for pickling to which has been added a small proportion of a product made by extracting petroleum products with liquid sulphur dioxide and thereafter treating the extracted material with a sulphonating agent while dissolved in a substantial proportion of liquid sulphur dioxide.

7. A process for pickling metals which are easily corrodible which comprises treating the metals in an acid pickling bath containing, as an inhibitor, a material obtained from a mineral oil by solvent extraction with a selective solvent which tends to dissolve certain constituents of the oil and not to dissolve others, the constituents which the solvent tends to dissolve being generally those of an unsaturated nature, including those of an aromatic nature, and sulphonating the extract while in solution in liquid sulphur dioxide.

8. A process for pickling metals which are easily corrodible which comprises treating the metals in an acid pickling bath containing, as an inhibitor, 8. material obtained from a naphthene base crude oil by solvent extraction with a selective solvent which tends to dissolve certain preferential solvent, which tends to dissolve certain constituents of the petroleum products and not to dissolve others, the constituents which the solvent tends to dissolve being generally those I of an unsaturated nature, including those of an aromatic nature, fractionally distilling the extracted material in a vacuum over caustic soda, discarding fractions from at least one end of the boiling range of said material, treating the remaining fraction with a small proportion of sulphuric acid, separating the sludge formed, and sulphonating the treated extract while in solution in liquid sulphur dioxide.

10. A process for pickling metals which com- 

